The electromagnetic ultrasonic transducer is a new type of ultrasonic waves source and it mainly comprises elastic vibration slice, vibrating coil (or magnet conducting vibrating diaphragm) and magnetostatic coil (or permanent magnet). Its working principle is as follows: an electrified coil is affected by Lorentz Force in a magnetic field. When alternating current goes through the coil, the bulk and direction of force on the vibrating coil will vary accordingly. If the vibrating coil is fixed on the elastic vibration slice, the Lorentz Force on the vibrating coil makes the elastic vibration slice vibrate and accordingly the sound waves are transmitted therefrom. The electromagnetic horn is made by use of this principle.
Because the electromagnetic ultrasonic transducer has advantages of no contact with the surface of medium material, no need to apply acoustic coupling agent, good repeatability, high speed for detection, etc., it is widely employed in the field of nondestructive examinations. But the electromagnetic ultrasonic transducer used in ultrasonic examinations has a low frequency and the focusing is hard to be realized, thus, this kind of electromagnetic ultrasonic transducer for inspections cannot be applied to ultrasonic therapy directly.